| Paper: | FR-P2.6 |
| Session: | Instrument Calibration II |
| Time: | Friday, March 30, 17:20 - 17:40 |
| Presentation: |
Oral
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| Topic: |
Sensor calibration: |
| Title: |
Design and RF performance analysis of microwave radiometer calibration targets |
| Authors: |
Giuseppe Addamo; CNR | | |
| | Oscar Antonio Peverini; CNR | | |
| | Giuseppe Virone; CNR | | |
| | Ada Vittoria Bosisio; CNR | | |
| | Riccardo Tascone; CNR | | |
| | Luca Valenziano; INAF | | |
| | Andrea Di Cintio; OHB Italia | | |
| | Marco Grilli; OHB Italia | | |
| Abstract: |
Brightness temperature values observed by satellite microwave radiometers are employed in Earth Observation (EO) mission to derive geophysical observables such as vapor and liquid integrated content, rainfall occurrence, sea surface temperature, and so on.
The most common design for these radiometers is the total power scheme that requires - for the instrument calibration - targets with known and precise brightness temperature value. Hence, targets thermodynamic temperature gradients should be carefully minimized and their emissivity parameter should be as close to unity to have the brightness temperature approximately equal to the physical one.
On board calibration relies on observations of hot and cold reference targets towards the “end to end” calibration of the receiver. Satellite-borne radiometers point at the cosmic space to mimic the cold reference target but they still need a hot reference target to compute the calibration coefficients. Moreover, additional targets are generally required during the on-ground test to mimic both the scene and the cold sky in thermal vacuum chambers.
Here, the authors present a target whose design has the form of a periodic distribution of pyramids above a thick high-thermal-conductivity-metal baseplate characterized by high RF emissivity within a very compact size (tile dimensions are 0.2 m x 0.1 m). The pyramidal element geometry is invariant for rotation of 90° along the longitudinal axis thus showing the same electromagnetic behavior for both linear polarization. Very large target can be made with an array of tiles, each of them is composed by hundreds of unit cells (the pyramids).
The target RF parts are made out of an absorbing material, ECCOSORB CR117, with a properly shaped metal rod inserted in all pyramids to reduce the overall thermal gradient without impacting neither the RF nor the mechanical performance. The surface distribution of brightness temperature is used to compute the antenna temperature at the radiometer input. Within the Rayleigh –Jeans regime, valid from K to W band and in the temperature range of interest of EO applications, the brightness temperature of the target can be easily evaluated only for an isothermal body. This suggests the minimization of the overall thermal gradient across the target.
A multiphysics model developed at IEIIT that allows the calculation of the brightness temperature for a periodic configuration of non-isothermal elements based on their longitudinal physical temperature profile and the absorbed RF power distribution will be also presented at the conference.
This RF-thermal model is a computational tool useful for both the optimization of the pyramidal absorbers and the target brightness temperature prediction in actual operative conditions.
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